This invention relates to nuclear steam generating equipment, and particularly to fluid measurements in the various components thereof.
During normal steady state operation of steam generating systems having several heat exchange, fluid storage, heat generating and pressurizer components, important properties such as the mass of the fluid in the system, its state, and the distribution thereof, are usually uniquely determinable through direct measurement of liquid level, fluid flow rate, and a calculation of heat and mass balance. However, in nuclear power steam supply systems (NSSS), and especially in the pressurized water type having primary and secondary fluid loops, the continuous determination of the distribution and state of the fluid within the system during transient conditions is much more difficult. Under accident conditions, such as those encountered at the Three Mile Island nuclear plant in March, 1979, conventional instrumentation may be inadequate for providing continuous, useable data that can quickly characterize the fluid condition in the system so that corrective measures can be confidently implemented.
Such fluid characterization is essential with respect to the nuclear reactor vessel, which contains thousands of uraninum-bearing fuel rods. Even after the nuclear chain reaction is terminated by scramming the reactor at the onset of an accident, residual heat continues to be generated and must be removed from the fuel rods or rod melting may occur. If insufficient fluid is available in the vessel to absorb and transport the heat, the melting rods will release their highly radioactive content to the fluid and contaminate the reactor building. Accordingly, the paramount purpose of safety systems in nuclear reactor installations is the maintenance of core cooling capability by assuring that the liquid level therein is sufficient to at least cover the fuel.
Suitable liquid level indicators for nuclear reactor vessels are not readily available, as conventional devices cannot easily and reliably be adapted for the hostile and turbulent conditions which may occur in the vessel during a nuclear accident.